B

Bypass
Most of Bronkhorst's thermal mass flow meters/controllers operate on a
principle where the gas flow is split in
two, leading a small part through a sensor channel and the remainder through
the parallel main channel, in a constant ratio. Due to a perfect 'flow
split' the sensor indicates a highly accurate measuring value over the
entire range of the instrument.

C

CalibrationAdjusting an instrument so that its reading can be correlated
to the actual value being measured.

CVD
Chemical Vapor Deposition. Chemical
process whereby a gas flow reacts and deposits a thin, high purity film on
a substrate, e.g. a silicon wafer, but also used for surface hardening and
production of synthetic diamonds.

Coriolis principleDirect mass flow measuring principle
based on the 'Coriolis effect'. The Coriolis forces in a vibrating tube
cause changes in frequency, phase shift or amplitude. The output signal
of the sensor is proportional to the mass flow.

D

Differential pressure (ΔP)Pressure difference between two locations in a system, for instance
between the inlet and outlet of a measuring device or control valve, or
the ΔP between two fluid lines or vessels.

J

K

L

Laminar Flow ElementFlow obstruction in the main channel of a thermal mass flow meter/controller.
Due to the created pressure difference a proportional part of the flow
is lead through the sensor channel, in parallel to the main channel.

Load impedance
The impedance presented to the electrical connector of an instrument.

LVDLow Voltage Directive.
European directvie 2006/95/EC, relating to electrical equipment designed
for use within certain voltage limits, is applicable to Bronkhorst®
Power Supply devices. See our Certificates
and Declarations.

M

ManifoldBase block on which a variety of functional modules for gas flow,
liquid flow or pressure measurement/control as well as filters and mixing
chambers can be mounted or integrated.

MassQuantity of substance expressed in (kilo)gram.

MFCMass Flow Controller.
Combination of a mass flow meter with a control valve for control of gas
or liquid flows.

Repeatability
The variability span for the measuring value when measurements are consecutively repeated
under the same conditions.

Response time
Time required for the output of a measuring device to change from its previous
state to a final settled value within a tolerance band of the correct new
value.

RoHSRestriction of Hazardous
Substances. Directive 2002/95/EC on the restriction of
the use of certain hazardous substances in electrical and electronic equipment.
See our Certificates
and Declarations.

S

Settling timeThe time required for a (flow or pressure) controller to settle
and remain at a given value once an input signal is received.

Surface Mount / Top-mountMounting of an instrument on the surface of a base block (e.g.
a manifold), due to which the tubing need not be dismounted in case of
inspection or exchange of the device.

T

Thermal principleMeasuring principle whereby flowing gas/liquid
(partially) gets heated, resulting in a temperature difference (ΔT) picked
up by two temperature sensors. This ΔT is proportional to the mass flow.
This principle is based on heat transfer and therefore dependent of the
density and specific heat of the fluid. Therefore thermal mass flow meters/controllers
need to be calibrated for a specific fluid. The effect of pressure or temperature
changes is relatively small, compared to volumetric flow measurement, however
for optimum accuracy it cannot be neglected. Conversion factors or additional
calibration curves may be helpful in this case.

Top-mount / Surface Mount
Mounting of an instrument on the surface of a base block (e.g. a manifold),
due to which the tubing need not be dismounted in case of inspection or
exchange of the device.

U

V

Volumetric flowFlow expressed in volume units per time units. The only flow meter
technology that measures volume directly is the positive displacement flow
meter.

W

X

Y

Z

Zero drift
Offset from the true zero. Slow and usually non-periodic change of the
zero point of a measuring instrument.